Semiconductor Laser Diode

ABSTRACT

A semiconductor laser diode is provided. In an embodiment the semiconductor laser diode includes a semiconductor layer sequence having semiconductor layers disposed vertically one above the other. An active layer includes an active region having a width of greater than or equal to 30 μm emitting laser radiation during operation via a radiation coupling-out surface. The radiation coupling-out surface is formed by a lateral surface of the semiconductor layer sequence and forms, with an opposite rear surface, a resonator having lateral gain-guiding in a longitudinal direction. The semiconductor layer sequence is heated in a thermal region of influence by reason of the operation. A metallization layer is in direct contact with a top side of the semiconductor layer sequence.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. application Ser. No.14/361,647, entitled “Semiconductor Laser Diode” which was filed on May29, 2014 and issued as U.S. Pat. No. 9,722,394 on Aug. 1, 2017 which isa national phase filing under section 371 of PCT/EP2012/073004, filedNov. 19, 2012, which claims the priority of German patent application 102011 055 891.8, filed Nov. 30, 2011, all of which are incorporatedherein by reference in its entirety.

TECHNICAL FIELD

A semiconductor laser diode is provided.

BACKGROUND

High-power laser diode chips which are produced from a semiconductormaterial which is epitaxially deposited on a substrate are mounted onheat sinks or carriers to ensure sufficient heat dissipation. The heatsinks or carriers have a high thermal conductivity and partly also anactive cooling, i.e., a flow of a coolant. Mounting is typicallyaffected by soldering. For this purpose, the laser diode chips have, onthe mounting surface, a metallization having a large area which is usedas soldering surface.

The sources of heat losses in high-power laser diode chips of a typicaldesign having asymmetric mirror reflectivities and one or more emitterstrips are not uniformly distributed. Rather, the sources of heat lossesare concentrated on the electrically contacted emitter strips to thegreatest extent in the resonator direction close to the coupling-outbevel and in a lateral direction transverse to the resonator directionin the semiconductor material. The heat losses are dissipated by thermalconduction from the chip via the metallization forming the solderingsurface and via the solder to the heat sink or to the carrier. The pathsof electrical current and heat flow are in this case typically virtuallyidentical.

With respect to temperature management, typical high-power laser diodechips are provided, for the greatest possible heat dissipation, with athermal bonding surface, which is as large as possible, between thesemiconductor chip and the heat sink or the carrier, i.e., with ametallization forming the soldering surface having a greatest possiblearea. As a result, the thermal resistance of a laser diode chip shouldbe kept as low as possible since important laser parameters can benefittherefrom during operation, for instance, high efficiency, low beamdivergence, higher power rating and greater reliability. Against thisbackground, the minimum size for the thermal bonding surface which is tobe meaningfully selected approximately corresponds to the region of theexpansion of the region producing the heat losses or is somewhat largerowing to heat spreading effects in the semiconductor material.

However, in comparison with the heat sink material or carrier material,the soldering boundary surface typically has a large thermal transferresistance, whereby in typical laser diode chips a temperature profilecan arise which produces a thermal lens owing to the aforementionedinhomogeneous distribution of the heat losses by the temperaturedependency of the refractive index and optical gain. This has theconsequence that in the case of larger operating currents or outputpowers, the beam divergence of known laser diode chips is increased.

However, in the known approach of thermally bonding the semiconductormaterial to a heat sink or a carrier over a surface as large aspossible, the optimization of several laser parameters reaches a limitsince although the absolute level of the temperature in thesemiconductor material can be reduced, the basic inhomogeneity of thetemperature distribution is retained. There are no known methods forsuppressing the thermal lens produced by the inhomogeneity, except forthe optimization of the efficiency of the laser which is in any caseperformed in a typical manner.

SUMMARY

Particular embodiments provide a semiconductor laser diode in whichinhomogeneity in the temperature distribution is reduced compared withknown laser diodes.

In accordance with at least one embodiment, a semiconductor laser diodehas a semiconductor layer sequence having semiconductor layers appliedvertically one above the other. The individual semiconductor layers havea lateral or transverse direction directed perpendicular to the verticalgrowth direction and a longitudinal direction perpendicular to thevertical direction and to the lateral direction. In particular, thesemiconductor layer sequence has an active layer which generates laserradiation in an active region during operation. The laser radiation isemitted via a radiation coupling-out surface during operation, whereinthe radiation coupling-out surface is formed by a lateral surface of thesemiconductor layer sequence and forms, with an opposite rear surface ofthe semiconductor layer sequence, a resonator in the longitudinaldirection. The semiconductor laser diode described herein is thuspreferably a so-called edge-emitting semiconductor laser diode.

A metallization layer is applied in direct contact with a top side ofthe semiconductor layer sequence, wherein the top side of thesemiconductor layer sequence is formed by a semiconductor cover layer.In other words, the semiconductor cover layer is the semiconductor layerwhich is uppermost in the semiconductor layer sequence in the verticaldirection.

A structured heat-dissipating layer is also applied to the top side ofthe semiconductor layer sequence. The structured heat-dissipating layerhas at least the metallization layer.

Furthermore, the active region of the semiconductor laser diode has awidth of greater than or equal to 30 μm. Such a semiconductor laserdiode can also be referred to as a so-called stripe laser, and in aparticularly preferred manner as a so-called broad stripe laser.Furthermore, the width of the active region can be less than or equal to200 μm and in a particularly preferred manner greater than or equal to50 μm and less than or equal to 150 μm. In one preferred embodiment, theactive region can have a width of approximately 100 μm. The width of theactive region is determined substantially by the width of asemiconductor layer defining the lateral current expansion taking intoaccount current expansion effects in the semiconductor layers. Thislayer, preferably formed in a strip-like manner, is referred to in thiscase as the current-supplying semiconductor layer and can be formed bythe semiconductor cover layer and/or one or more underlying layers.

The resonator of the semiconductor layer sequence is a resonator havingat least predominately lateral gain-guiding. In other words, in the caseof the semiconductor laser diode described herein, the lateralgain-guiding is predominant over lateral index-guiding in the resonatorwhich could be achieved, for example, by a ridge structure close to theactive layer in the semiconductor layers arranged above the activelayer. The principles of lateral gain-guiding and lateral index-guidingare known to the person skilled in the art and are therefore notdescribed further. An example of a semiconductor laser which, incontrast to the semiconductor laser diode described herein, haspredominately lateral index-guiding, can be a trapezoidal ridgewaveguide laser known to the person skilled in the art. A resonatorhaving predominately lateral gain-guiding will be abbreviatedhereinafter to resonator having lateral gain-guiding.

By operating the semiconductor laser diode, the semiconductor layersequence is heated during the generation of the laser radiation in aregion which is referred to here and hereinafter as a thermal region ofinfluence. The thermal region of influence of the semiconductor laserdiode described herein extends in the longitudinal direction in eachcase to about 50 μm to the radiation coupling-out surface and the rearsurface. In the lateral direction, the thermal region of influence, asseen from the center of the active region, is defined by the distancefrom the center of the active region, at which the temperature hasfallen to a value of Tmin+(Tmax−Tmin)/10, wherein Tmax and Tmin are theoverall maximum and overall minimum values of the temperature in theregion between the lateral center of the active region and the lateraledge of the semiconductor layer sequence. In the case of a semiconductorlaser diode having a plurality of active regions, which are arrangednext to each other in the lateral direction, Tmin designates the overallminimum value of the temperature between two adjacent active regions.

Heating of the semiconductor layer sequence outside of the previouslydefined thermal region of influence, e.g., directly on the radiationcoupling-out surface and the rear surface, is not consideredhereinafter.

The width of the thermal region of influence depends upon the width ofthe active region and thus upon the width of the region in the activelayer into which current is injected. Owing to the heat spreadingeffects in the semiconductor layer sequence, the thermal region ofinfluence is always wider than the active region. Typically, the widthof the thermal region of influence is smaller than the width of theactive region plus approximately 2×50 μm. In other words, the thermalregion of influence protrudes beyond the active region in the lateraldirection on both sides in each case by less than 50 μm.

The metallization layer further comprises a cumulative width in theregion above the thermal region of influence. In the case of ametallization layer which is locally contiguous in its width andunstructured, the cumulative width corresponds to the width of themetallization layer. If the metallization layer has, in the lateraldirection in one region a structuring, e.g., openings, a half-tone-likestructured edge or wedge-shaped cut-outs as described further below,then the cumulative width designates the sum of the widths of allpartial pieces in this region.

In the case of the semiconductor laser diode described herein, the ratioof the cumulative width of the metallization layer to the width of thethermal region of influence varies in dependence upon a distance to theradiation coupling-out surface, wherein the cumulative width and thewidth of the thermal region of influence are to be used for the ratio atthe same distance to the radiation coupling-out surface. The structuredheat-dissipating layer thus permits heat dissipation from the activeregion which varies along a longitudinal and/or lateral direction.

Owing to the varying ratio of the cumulative width of the metallizationlayer and the width of the thermal region of influence in thelongitudinal direction, the local thermal resistance can thus be variedfor heat dissipation from the thermal region of influence of thesemiconductor layer sequence. The local thermal resistance designateshere and hereinafter a variable which is proportional to the quotientfrom the local temperature increase in the active region of thesemiconductor laser diode and the local loss factor density which occursduring operation of the semiconductor laser diode. The local thermalresistance is thus a measurement of the extent to which a sub-region ofthe active region is heated by operation of the semiconductor laserdiode owing to the current injection into the active region and thelocal loss factor density produced thereby. The higher the local thermalresistance, the higher the local temperature increase becomes at aparticular local loss factor density and vice-versa. The local thermalresistance is lower the higher the heat dissipation through thestructured heat-conducting layer and is thus also a measurementparticularly for the heat dissipation thereof since the local thermalresistance and thus the local temperature increase at a local lossfactor density are lower the higher the corresponding local heatdissipation through the structured heat-dissipating layer.

In the case of thermal bonding over a large area through anon-structured heat-dissipating layer, as this is the case in knownlaser diode chips, the local thermal resistance for the heat dissipationis at least substantially homogeneous everywhere so that a highertemperature increase is produced at locations with a higher local lossfactor density than at locations with a lower loss factor density whichresults in the above-described inhomogeneous temperature distributionparticularly in the thermal region of influence. In the case of thesemiconductor laser diode described herein, the structuring of thestructured heat-dissipating layer and in particular of the metallizationlayer can advantageously be selected such that in the thermal region ofinfluence the local thermal resistance is adapted to the local lossfactor density and is higher in sub-regions in which the local lossfactor density is lower than in other sub-regions.

The fact that a layer or an element is arranged or applied “on” or“over” another layer or another element can mean here and hereinafterthat said layer or said element is directly arranged in directmechanical and/or electrical contact on said other layer or said otherelement. Furthermore, it can also mean that said layer or said elementis arranged indirectly on or over said other layer or said otherelement. Further layers and/or elements can then be arranged betweensaid layer and said other layer or between said element and said otherelement.

The fact that a layer or an element is arranged “between” two otherlayers or elements can mean here and hereinafter that said layer or saidelement is directly arranged in direct mechanical and/or electricalcontact or in indirect contact with respect to one of the two otherlayers or elements and in direct mechanical and/or electrical contact orin indirect contact with respect to the other one of the two otherlayers or elements. In the case of indirect contact, further layersand/or elements can then be arranged between said one layer and at leastone of the two other layers or between said one element and at least oneof the two other elements.

In accordance with the above statements, the semiconductor layersequence has semiconductor layers which each extend along a main plane,wherein the main plane is spanned by the longitudinal and lateral ortransverse directions whilst the arrangement direction or growthdirection of the semiconductor layer sequence defines the verticaldirection of the semiconductor laser diode. If a width, e.g., of asemiconductor layer sequence, of another layer or region is mentionedhereinafter, then this is intended to mean the extent of the relevantelement in the lateral or transverse direction. Length refers to theextent in the longitudinal direction whilst thickness or heightdesignates the extent in the vertical direction.

In accordance with a further embodiment, the semiconductor layersequence has, in addition to the active layer, further functionalsemiconductor layers, e.g., waveguide layers, shell layers, bufferlayers and/or semiconductor contact layers. As the active region, thesemiconductor layer sequence can have, for example, a conventionalpn-junction, a double heterostructure or a single or multiple quantumwell structure. The quantum well structure can comprise, for example,quantum wells, quantum wires or quantum dots or combinations of thesestructures.

The semiconductor layer sequence can have, for example, one or severalsemiconductor layers consisting of an arsenide, phosphide or nitridesemiconductor material. For long-wave, infrared to red radiation, asemiconductor layer sequence on the basis of In_(x)Ga_(y)Al_(1-x-y)As issuitable, for example, for red radiation, a semiconductor layer sequenceon the basis of In_(x)Ga_(y)Al_(1-x-y)P is suitable, for example, andfor short-wave, visible radiation, i.e., in the range of green to bluelight, and/or for UV radiation, a semiconductor layer sequence on thebasis of In_(x)Ga_(y)Al_(1-x-y)N is suitable, for example, wherein ineach case 0≦x≦1 and 0≦y≦1.

The semiconductor layers of the semiconductor layer sequence arepreferably grown on a substrate such that the semiconductor layersequence terminates on the side, facing away from the substrate, withthe semiconductor cover layer. After the layers are grown, the substratecan be completely or partially removed. Furthermore, electrode layersare provided on the semiconductor layer sequence for contacting thesemiconductor layers. Preferably, the metallization layer, which is indirect contact with the semiconductor cover layer, forms such anelectrode layer. The semiconductor cover layer thus preferably forms asemiconductor contact layer which, in a particularly preferred manner,can be highly doped, in particular with a dopant concentration of morethan 1×10¹⁸ cm⁻³. Typically, for this purpose, the semiconductor coverlayer can have a thickness in the range of about 200 nm. Depending uponthe transverse conductivity of the semiconductor cover layer, this canalso have a larger or smaller thickness. The side of the semiconductorlayer sequence facing away from the metallization layer can be contactedby a further electrode layer.

Furthermore, a passivation layer can be arranged, for example, at leastin sub-regions on the top side of the semiconductor layer sequence,which passivation layer is structured such that the metallization layercan directly contact the top side of the semiconductor layer sequenceonly in a sub-region, in particular in the region of the semiconductorcover layer. The semiconductor cover layer can be, for example,structured and removed in sub-regions. In this case, the top side of thesemiconductor layer sequence is formed, in the regions in which thesemiconductor cover layer is removed, by the underlying exposedsemiconductor layer.

Furthermore, the semiconductor layer sequence can have, between thestructured heat-dissipating layer and the active region, a semiconductorlayer supplying current to the active region. The current-supplyingsemiconductor layer can be structured and have a lateral width whichvaries in the longitudinal direction. For example, the width of thecurrent-supplying layer can become smaller as the distance to theradiation coupling-out surface increases which means that thecurrent-supplying layer has a trapezoidal structure. Alternatively, thecurrent-supplying layer can have a width which becomes larger at leastin a sub-region as the distance to the radiation coupling-out surfacebecomes larger. By varying the width of the current-supplying layer, thewidth of the thermal region of influence is also varied.

For example, the current-supplying layer can be structured as previouslydescribed and can comprise, or be formed by, the semiconductor coverlayer. Alternatively or in addition, it is also possible that thestructured current-supplying semiconductor layer comprises, or is formedby, a semiconductor layer arranged between the active layer and thesemiconductor cover layer. The structured current-supplyingsemiconductor layer can thus preferably form a strip in the longitudinaldirection, which strip extends from the radiation coupling-out surfaceto the rear surface opposite the radiation coupling-out surface. In thecase that the current-supplying semiconductor layer has a width whichbecomes smaller or larger at least in a sub-region as the distance tothe radiation coupling-out surface becomes larger, the width of thecurrent injection and thus the width of the region in which a local lossfactor density is produced, can be varied in dependence upon thedistance to the radiation coupling-out surface. In particular, in thecase of a current-supplying layer which becomes narrower towards theradiation coupling-out surface, the current density and thus also thelocal loss factor density in the active layer can close to the radiationcoupling-out surface be smaller than at a larger distance to theradiation coupling-out surface. In this case, it can be advantageouslypossible to influence the temperature distribution in particular in theactive region and in the surrounding semiconductor layers. By reducingthe current density close to the radiation coupling-out surface, it canbe possible to lower the increased temperature, which occurs in typicallaser diodes, at the radiation coupling-out surface.

Furthermore, the contact surface between the metallization and the topside of the semiconductor layer sequence, which is formed by an openingextending in the longitudinal direction in a passivation layer arrangedon its top side, can, for example, be narrower and in shape independentof the width and/or of the structuring of the current-supplying layer.

In accordance with a further embodiment, at least one semiconductorlayer has a structured edge between the semiconductor cover layer andthe active layer in the lateral direction. The edge in the lateraldirection is thus the edge delimiting or defining the width of thesemiconductor layer and extends in the longitudinal direction. Inparticular, the semiconductor layer having the structured edge can bearranged between the structured current-supplying semiconductor layerand the active layer. For example, the edge can be structured in aserration-like manner. By way of such structuring, the current expansionand thus the extent of the active region in the active layer can beinfluenced in an advantageous manner.

In accordance with a further embodiment, the metallization layercomprises one or, in a particularly preferred manner, a plurality oflayers which each consist of a metal or an alloy. Therefore, themetallization layer can have a vertical structure in the form of theplurality of layers. The total thickness of the metallization layer canbe up to a few micrometers. For example, the metallization layer canhave a layer sequence having the materials Ti/Pt/Au or AuGe/Ni/Au. Thelayers of the metallization layer can be selected in particular on thebasis of producibility, mechanical adhesion between the metal and thetop side of the semiconductor layer sequence and the electrical contactresistance of the metal-semiconductor transition.

In accordance with a further embodiment, the structured heat-dissipatinglayer is formed by the metallization layer. In other words, this meansthat the metallization layer effects, owing to a structuring in thelateral and/or longitudinal direction in the thermal region ofinfluence, a local thermal resistance along a longitudinal and/orlateral direction which varies.

In accordance with a further embodiment, the ratio of the cumulativewidth of the metallization layer to the width of the thermal region ofinfluence decreases as the distance to the radiation coupling-outsurface increases. As a result it can be achieved that as the distanceto the radiation coupling-out surface increases, the bonding surface ofthe semiconductor layer sequence formed by the metallization layerbecomes smaller in relation to the thermal region of influence whichmeans that as the distance to the radiation coupling-out surfaceincreases, there is a lower amount of heat dissipation. In comparison tothe known unstructured bonding over a large area by an unstructuredmetallization over a large area, the temperature is thereby increased insub-regions of the semiconductor layer sequence as the distance to therear surface becomes smaller so that temperature differences in theresonator direction can be reduced.

In particular, the metallization layer can have varying structuringand/or a varying width in dependence upon a distance to the radiationcoupling-out surface. The varying structuring and/or the varying widthpreferably can be different, at least in a sub-region, from structuringand/or a width of the semiconductor layers of the semiconductor layersequence which are arranged between the metallization layer and theactive layer. In particular, this can mean that the metallization layerand the semiconductor layers arranged above the active layer, i.e., inparticular, for example, the semiconductor cover layer do not form aridge waveguide structure having identical layer cross-sections in thelateral and longitudinal direction, as this is the case in known ridgewaveguide lasers.

In accordance with a further embodiment, the metallization layer has awidth which decreases as the distance to the radiation coupling-outsurface increases. In other words, the metallization layer becomesnarrower as the distance to the radiation coupling-out surfaceincreases. Consequently, as already explained previously, the surface,by means of which the semiconductor laser diode can be arranged on anexternal carrier or an external heat sink, e.g., by soldering, can bereduced as the distance to the radiation coupling-out surface increases.The heat dissipation through the metallization layer thus becomes loweras the distance to the radiation coupling-out surface increases, wherebythe local thermal resistance increases correspondingly. For example, themetallization layer can be wider, close to the radiation coupling-outsurface, than the current-supplying semiconductor layer and inparticular wider than the thermal region of influence. The phrase “closeto the radiation coupling-out surface” refers to the end, facing theradiation coupling-out surface, of the metallization layer in thelongitudinal direction. Close to the rear surface, the metallizationlayer can be narrower than the thermal region of influence andfurthermore also narrower than the current-supplying semiconductorlayer.

In accordance with a further embodiment, the metallization layer hasopenings, in particular, for example, openings which are arranged overthe current-supplying layer in the vertical direction, wherein theopenings can take up a larger surface area as the distance to theradiation coupling-out surface increases. This can mean that as thedistance to the radiation coupling-out surface increases, the size,number, density or a combination of these characteristics becomesgreater. As a result, the cumulative width of the metallization layerbecomes smaller as the distance to the radiation coupling-out surfaceincreases.

In accordance with a further embodiment, a material is arranged in theopenings which has a lower thermal conductivity than the metallizationlayer. Furthermore, it can also be possible that a material is arrangedin the openings which has a lower solderability than the metallizationlayer. Lower solderability can mean in particular that a higher thermalresistance is achieved at the solder boundary surface. As a result, inthe region of the openings a lower thermal conductivity and thus a lowerheat dissipation of the heat produced in the active region to a heatsink arranged on the metallization can be made possible. The materialcan be formed, e.g., by a synthetic material, e.g., benzocyclobutene(BCB), by air or even by a vacuum. Furthermore, it is also possible thatthe material in the openings is formed by a material which cannot besoldered, or cannot be soldered very effectively, e.g., a metal whichcannot be soldered very effectively, for instance an oxidized metal. Itcan also be possible that the metallization is produced without openingsand the metallization is then oxidized in mutually separate sub-regions,wherein the surface density of the oxidized sub-regions increases as thedistance to the radiation coupling-out surface increases.

In accordance with a further embodiment, the metallization layer has anedge in the lateral direction which is structured in an insular manner.The edge in the lateral direction refers to the edge of themetallization layer by means of which the width of the metallizationlayer is determined and which extends in the longitudinal direction. Anedge having insular structuring can mean in particular that a centralstrip is arranged in the longitudinal direction over the active regionand the metallization layer has, in the lateral direction, islands inaddition to the central strip. As the lateral distance to the centralstrip increases, the islands can preferably have a smaller surfacedensity, i.e., can have one or more characteristics selected from size,number and density which become smaller as the lateral distance to thecentral strip increases. The structured edge in the lateral direction ofthe metallization layer can, in a particularly preferred manner, bestructured in a half-tone-like manner. Furthermore, it can also bepossible that the edge in the lateral direction has openings whichbecome larger as the lateral distance increases as seen from the centerof the metallization layer and/or increase in number and/or density.

In accordance with a further embodiment, an internal heat sink isapplied to the metallization layer in direct contact. An internal heatsink or integrated heat sink is intended to mean here and hereinafter aregion or a layer which is applied directly to the metallization layerdirectly and preferably without a solder connection and has, at least ina sub-region, a preferably high thermal conductivity. In contrast to anexternal heat sink or a carrier on which the semiconductor laser diodeis soldered, the internal heat sink is thus part of the semiconductorlaser diode and is preferably applied to a plurality of semiconductorlaser diodes in the form of a wafer composite thereon, is optionallystructured and is separated with the wafer composite. By means of theinternal heat sink, the thermal resistance can be lowered between thesemiconductor layer sequence and an external heat sink since thecritical boundary surface with respect to the heat dissipation, formedby the solder surface between the semiconductor laser diode and anexternal heat sink or an external carrier having typically extremelyhigh thermal contact resistances, can be arranged further away from thesemiconductor layer sequence and thus further away from the activeregion. By way of the high thermal transverse conductivity, the heatpath in the layer thickness additionally obtained by the internal heatsink is effectively spread within the internal heat sink in advance ofthe solder boundary surface and the thermal resistance is thus reduced.In particular, the internal heat sink can have a solder side facing awayfrom the semiconductor layer sequence, via which the semiconductor laserdiode can be mounted on an external carrier by a solder layer.

In accordance with a further embodiment, the internal heat sink is notstructured in the lateral and longitudinal direction and thus has ahomogeneous thermal conductivity in the lateral and longitudinaldirection. The varying local thermal resistance in the longitudinaland/or lateral direction can thus be predetermined by the structuredmetallization layer in accordance with the preceding embodiments, whilstthe integrated heat sink merely lowers the total heat resistance of thesemiconductor laser diode.

In accordance with a further embodiment, the structured heat-dissipatinglayer additionally comprises the internal heat sink, wherein theinternal heat sink has structuring at least in the lateral and/orlongitudinal direction. In other words, the internal heat sink can bepart of the structured heat-dissipating layer.

The structuring of the internal heat sink can be formed, for example, bymaterials having different thermal conductivities, which are arranged ina structured manner in the lateral and/or longitudinal direction.Additionally, the internal heat sink can also have structuring in thevertical direction. For example, the integrated heat sink can compriseone or several metals, for example, selected from Au, Ag, Cu and Ni,alloys, for example, CuW, dielectric materials, for example, an oxide ora nitride such as for instance silicon oxide or silicon nitride, apolymer, for example, BCB, a crystalline semiconductor such as forinstance AlN, an amorphous semiconductor such as for instance Si or Ge,diamond, a ceramic material, air or vacuum. The material(s) of theinternal heat sink can be applied on the metallization layer, forexample, by vapor deposition, sputtering, galvanic deposition, plasmadeposition, spin-coating or bonding.

In a particularly preferred manner, the internal sink comprises at leasttwo materials having greatly different thermal conductivities, whereby acontrast-rich thermal profile can be achieved. The degrees of freedom,formed by the structural geometry and the material selection, for thedesign of the internal heat sink allow the thermal conductivity profileto be adjusted extensively, whereby optimization of the laser parametersof the semiconductor laser diode can be achieved. The internal heat sinkcan have a thickness of a few hundred nanometers and preferably 1 μm ormore. In a particularly preferred manner, the internal heat sink isapplied by galvanic deposition when using metallic materials and at athickness of more than 2 μm. The internal heat sink can be used, in thecase of electrically conductive materials, to supply electricity for themetallization layer. If non-electrically conductive materials are usedfor the internal heat sink, then an electric supply element, e.g., inthe form of electric bushings, is provided, by means of which anelectric parallel path, in addition to the thermal path, is achieved.The electric parallel path preferably has a low supply resistance withrespect to the semiconductor layer sequence.

The thickness of the integrated heat sink should not be less than aminimum thickness in dependence upon the thermal conductivity of thematerials used. In the case of gold, for example, the minimum thicknessshould be 1 μm, preferably at least 2 μm and, in a particularlypreferred manner, at least 5 μm.

Furthermore, it can also be possible that the semiconductor laser diodeis applied to a structured external heat sink. However, the use of aninternal heat sink is advantageous in that the thermally poor solderboundary surface is further away from the semiconductor layer sequence,whereby a lower overall thermal resistance is achieved. Furthermore, inthe case of an internal heat sink, there is also no requirement forprecise adjustment of the semiconductor laser diode when mounting on apre-structured external heat sink.

In accordance with a further embodiment, it may be necessary, to avoiddisadvantages in the production and/or during operation of thesemiconductor laser diode, that one or more materials have to beencapsulated with respect to the surroundings. Such disadvantages may becaused, for example, by oxidation in air, e.g., in the case of copper,by the diffusion of materials into the semiconductor and thus a changein the properties of the semiconductor layer sequence, e.g., in the caseof copper, silver or gold, or by metallurgical reactions betweendifferent metals. Barriers consisting of enclosed layers can be used,for example, as the encapsulation. For example, platinum or chromium canbe used to encapsulate gold and, for example, nickel can be used in thecase of copper.

Furthermore, a thin-layer encapsulation can be used to encapsulate amaterial to be encapsulated. A barrier effect is produced in the case ofthe thin-layer encapsulation substantially by barrier layers and/orpassivation layers designed as thin layers. The layers of the thin-layerencapsulation generally have a thickness of less than or equal to a few100 nm. The thin layers can be applied, for example, by an atomic layerdeposition (ALD) process. Suitable materials for the layers of theencapsulation arrangement are, for example, aluminum oxide, zinc oxide,zirconium oxide, titanium oxide, hafnium oxide, lanthanum oxide.Preferably, the encapsulation arrangement comprises a layer sequencehaving a plurality of thin layers which each have a thickness betweenone atom layer and to nm inclusive.

Preferably, the internal heat sink is applied by galvanic deposition. Asa result, it can be possible to apply metallic layers and/or regions atroom temperature or at the subsequent operating temperature of thesemiconductor laser diode. Therefore, the finished component can haveonly very small bracings which can be very advantageous, e.g.,especially in the case of thick metallic layers as preferred for theinternal heat sink. If, as is typical in the prior art, metals aredeposited by vapor deposition or sputtering namely at increasedtemperatures, then large bracings can be present in the finishedcomponent after cooling to room temperature owing to the differentthermal expansion coefficients between the materials used, i.e.,semiconductor materials, dielectric materials, metals and/or syntheticmaterials. Examples of expansion coefficients are: 6×10⁻⁶/K for galliumarsenide, 1.6×10⁻⁵/K for copper and 1.9×10⁻⁵/K for silver. Large bracingcan result in the performance being impaired, in particular in view ofthe polarization purity, the efficiency and the divergency, and thereliability of the semiconductor laser diode.

In accordance with a further embodiment, the internal heat sink has aregion having a first material which is arranged in the lateraldirection between two further regions each having a second material. Thesecond material can have a different, and preferably lower, thermalconductivity than the first material. In addition, it can also bepossible that the first and second material alternate in the verticaldirection, e.g., that the second material is arranged in the verticaldirection between regions of the first material. The second materialand/or the first material can also have a wedge shape, wherein, forexample, the thickness of the second material increases as the lateraldistance increases as seen from a center of the internal heat sink.Furthermore, it can also be possible that, for example, the firstmaterial has a width which decreases as the distance to the radiationcoupling-out surface increases. Furthermore, it can also be possiblethat the second material is embedded in the first material, e.g., in theform of a plurality of mutually separate sub-regions. Moreover, a thirdmaterial can also be provided, for example, and has a thermalconductivity different from the first and second material and isarranged at least partly as described previously for the first or secondmaterial.

In accordance with a further embodiment, the internal heat sink can havea smaller length in the longitudinal direction than the semiconductorlayer sequence, so that in the region of the radiation coupling-outsurface and/or in the region of the rear surface opposite the radiationcoupling-out surface the semiconductor layer sequence can have aprotrusion over the first material of the heat sink. A second material,for example, having a higher thermal conductivity than the firstmaterial, can be arranged in the region of the protrusion. The secondmaterial can further be formed from a material melting at a lowtemperature, in particular at a lower temperature than the firstmaterial and having a high thermal conductivity. For example, the secondmaterial can be formed by a metal such as, for example, indium having amelting point of approximately 157° C. or tin having a melting point ofapproximately 230° C. The second material can be applied in the form ofa deposition in the region of the protrusion. As a result, it can bepossible to produce a plurality of semiconductor laser diodes in a wafercomposite having internal heat sinks with the first and second materialformed as a deposition and then to separate the individual semiconductorlaser diodes. Separation can be effected, for example, by breaking thewafer composite to produce laser bevels. After separation, by heating toabove the melting point of the second material, a self adjusted channelof the second material can be formed from the deposition so that areduction in the local thermal resistance is produced close to theradiation coupling-out surface by the second material and the transitionto the first material in the longitudinal direction. The channel can beformed to be concave or convex depending upon the material, providedamount and dimension and process parameters.

In contrast to known laser diode chips in which a connection surfacewhich is as large as possible is provided in order to minimize thethermal resistance on the whole, in the semiconductor laser diodedescribed herein it can be particularly possible to vary the localthermal resistance between the semiconductor layer sequence and anexternal heat sink by way of the above-described structuring of theheat-dissipating layer, whereby inhomogeneity of the temperaturedistribution within the semiconductor layer can be reduced in thethermal region of influence. As a result, it can be possible to reduce,on the whole, the power of a thermal lens produced by temperatureinhomogeneities, although the total thermal resistance of thesemiconductor laser diode and also the absolute temperature level of thesemiconductor layer sequence can also be increased compared with knownlaser diode chips.

In accordance with the above-mentioned embodiments, the describedadvantageous effects can be achieved in particular by partly decouplingand/or separating the electrical and thermal path in the semiconductorlaser diode which, in a particularly preferred manner, is designed as abroad stripe laser. This can be possible by the use of two-dimensionallyor three-dimensionally structured metallizations, i.e., themetallization layer or in addition also the internal heat sink, on thesolder boundary surface and further, for example, in addition also by ahighly-conductive, laterally and longitudinally structured semiconductorlayer, e.g., the semiconductor cover layer. As a result, in the thermalregion of influence the distributions of electrical current and heatflow can be influenced within certain limits in a mutually independentmanner so that the temperature distribution in the semiconductor laserdiode can be varied independently of electric parameters and preferablycan be homogenized. As described further above, the two-dimensionally orthree-dimensionally structured metallization on or close to thesemiconductor layer sequence top side can comprise one or more differentmetals and/or additional materials such as air, vacuum or dielectricmaterials having different thermal conductivities, so that the thermalconductivity contrast between structured and unstructured regions can beincreased. By way of the structuring, the surface thermally connected toan external heat sink or an external carrier can become smaller, wherebythe overall thermal resistance of the semiconductor laser diode canincrease compared with a case without structuring, whereby however thethickness of the thermal lens can also be reduced.

The above-described monolithic integration of an internal heat sink canalso be particularly advantageous, for example, in the form of a thickmetallization having high thermal conductivity in order to move thethermally poorly conductive solder boundary surface between an externalheat sink or an external carrier and the semiconductor layer sequencefurther away from the main loss factor source, i.e., the active region,and to lower the overall thermal resistance of the semiconductor laserdiode by the thereby improved possible heat spreading. As a result, thepreviously described increase in the thermal resistance, caused by thestructuring of the metallization, can also be at least partlycompensated.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, advantageous embodiments and developments areapparent from the exemplified embodiments described hereinafter inconjunction with the figures, in which:

FIGS. 1A and 1B show a schematic sectional illustration and a schematicplan view of a laser diode;

FIG. 1C shows the dependency of the lateral far-field angle of thecoupled-out optical power in a laser diode of FIGS. 1A and 1B;

FIGS. 2A and 2B show schematic sectional illustrations of semiconductorlaser diodes in accordance with a few exemplified embodiments;

FIGS. 3A to 3D show schematic illustrations of plan views ofsemiconductor laser diodes in accordance with further exemplifiedembodiments;

FIGS. 4A and 4B show schematic illustrations of plan views ofsemiconductor laser diodes in accordance with further exemplifiedembodiments;

FIGS. 5 to 7 show schematic illustrations of plan views of semiconductorlaser diodes in accordance with further exemplified embodiments;

FIGS. 8 to 9C show schematic illustrations of plan views and sectionalillustrations of semiconductor laser diodes in accordance with furtherexemplified embodiments; and

FIGS. 10A to 11 show schematic illustrations of semiconductor laserdiodes in accordance with further exemplified embodiments.

In the exemplified embodiments and the figures, like or similar elementsor elements acting in a like manner can each be designated by equalreference numerals. The illustrated elements and the size ratios thereofwith respect to each other are not to be considered as being true toscale. Rather, individual elements, such as, for example, layers,components, devices and regions can be illustrated excessively large forease of reproducibility and/or for ease of understanding.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIGS. 1A and 1B show a typical high-power laser diode chip comprising asemiconductor layer sequence 2 which is epitaxially grown on a substrate1. FIG. 1A is a sectional illustration whilst FIG. 1B is a plan view.

The semiconductor layer sequence 2 comprises an active layer 23 havingan active region 24 which emits laser radiation via a radiationcoupling-out surface 11 during operation. The radiation coupling-outsurface 11 and the rear surface 12, opposite the radiation coupling-outsurface 11, of the semiconductor layer sequence 2 form a resonator andare at least partly provided with a silvering layer or antireflectivelayer. The semiconductor layers 21, 22, between which the active layer23 is arranged, can comprise, for example, waveguide layers and/or shelllayers and further semiconductor layers. In particular, the high-powerlaser diode chip illustrated in FIGS. 1A and 1B can be a typical broadstripe laser diode chip having lateral gain-guiding.

The arrangement direction of the semiconductor layers 21, 22, 23, 25 ofthe semiconductor layer sequence 2 refers in this case and in thefollowing figures to a vertical direction whilst the laser resonatorbetween the radiation coupling-out surface 11 and the rear surface 12opposite the radiation coupling-out surface 11 extends in thelongitudinal direction. A lateral or transverse direction is definedperpendicular to the longitudinal resonator direction in the mainextension plane of the semiconductor layers 21, 22, 23, 25.

Arranged above the active region 24 is a semiconductor cover layer 25which forms the top side 20 of the semiconductor layer sequence 2. Thesemiconductor cover layer 25 is electrically contacted by ametallization layer 3 which is applied over a large area to the top sideof the semiconductor layer sequence 2. Arranged between the regions ofthe semiconductor layer sequence 2 and the metallization layer 3, whichshould not be electrical contact with each other, is a passivation layer10, e.g., consisting of a dielectric material, for instance an oxide ora nitride.

The illustrated laser diode chip can be electrically connected andoperated via the metallization layer 3 and a further electrode layer forcontacting the side of the semiconductor layer sequence 2 (not shown)facing away from the metallization layer 3. The width of thesemiconductor cover layer 25, which in the case of broad stripe lasersis typically greater than or equal to 30 μm and less than or equal to200 μm, defines—in consideration of current expansion effects in theunderlying semiconductor layers 22—the width of the active region 24which thus likewise has a width of greater than or equal to 30 μm.

The laser diode chip illustrated in FIGS. 1A and 1B is formed as aso-called single emitter having an individual active region 24. Aso-called laser bar can also be formed by a corresponding lateralarrangement of several regions of the semiconductor cover layer 25contacted by the metallization layer 3, wherein the metallization layer3 is typically severed between the individual active regions so that theindividual active regions of the laser bar can be electrically operatedindependently of each other.

The progression of the semiconductor cover layer 25 is illustrated inFIG. 1B by the dotted line. Apart from current expansion effects, theprogression of the semiconductor cover layer 25 also corresponds to theprogression of the active region 24. By way of the current injectioninto the active layer 23 and thus the formation of the active region 24,a thermal region of influence 29 is also formed in the semiconductorlayer sequence 2 and is indicated in FIG. 1A in the active layer 23 andin FIG. 1B by the dashed region.

Laser diode chips in accordance with the example of FIGS. 1A and 1B aretypically soldered with the metallization layer 3 onto an external heatsink or a carrier having high thermal conductivity and/or activecooling. The metallization layer 3 is used as a solder surface of thelaser diode chip and allows the semiconductor layer sequence 2 to bethermally connected to the external heat sink or the carrier over alarge area. In particular, for example, for reasons of producibility,for instance in relation to the mechanical adhesion between metal andsemiconductor and the electrical contact resistance of themetal-semiconductor transition, the metallization layer 3 typically hasa plurality of metallic layers or layers having alloys, e.g., Ti/Pt/Auor AuGe/Ni/Au, having total layer thickness of up to a few micrometers.Whilst in a certain manner the metallization layer 3 is thus structuredin the vertical direction, in the laser diode chip illustrated in FIGS.1A and 1B it is divided in the lateral and longitudinal direction at themost to separate individual active regions in the case of a laser barwhen it is necessary to operate individual active regions of the laserbar in a mutually electrically separated manner. Furthermore, it canalso be possible that in the proximity of the radiation coupling-outsurface 11 or the rear surface 12, the metallization layer is withdrawntherefrom, i.e., is thinner than in the remaining region or iscompletely removed. Except for such structurings, brought about fortechnical reasons, the metallization layer 3 of the known laser diodechip covers the entire thermal region of influence 29 in a uniformmanner.

Whereas the metallization layer 3 in a typical laser diode chip, asshown in FIGS. 1A and 1B, thus allows to thermally bond in particularthe thermal region of influence 29 over a large area, the heat losssources in the semiconductor layer sequence 2 are not distributeduniformly, for example, owing to asymmetric mirror reflectivities of thesilvering layers or antireflective layers of the radiation coupling-outsurface 11 and the rear surface 12. In particular, known laser diodechips typically have a maximum temperature at the radiation coupling-outsurface 11 at the active region 24, which temperature decreases in thelongitudinal, vertical and lateral direction as the distance to theemission region increases. This is also true for a laser bar havingseveral active regions.

Whereas typically used external heat sinks or carriers itself have ahigh thermal conductivity compared with the semiconductor material, thesolder boundary surface produced during mounting typically has a highthermal transition resistance, e.g., when soldering with AuSn.Additionally a clearly poorer thermal conductivity of the soldermaterial is present compared with the material of the external heat sinkor the carrier itself. As a result, despite the high thermalconductivity of the external heat sink or of the carrier, a high thermalresistance is produced. The temperature profile formed in the knownlaser diode chip and the temperature dependency of the refractive indexand optical gain produce a thermal lens, whereby the divergence of theemitted laser radiation is increased. This means that as the operatingcurrents or output powers of the laser diode chip increase, the beamdivergence of the laser increases, as shown in FIG. 1C. FIG. 1C showsthe increase in the lateral far-field angle α in dependence upon thecoupled-out optical power which is present at the increasing thermalloading and the increasing inhomogeneity of the temperature distributionin the laser diode chip by forming the so-called thermal lens.

The semiconductor laser diodes of the exemplified embodiments of thefollowing figures have, proceeding from the known laser diode chip inFIGS. 1A and 1B and in contrast thereto, a structuring suitable tocounteract the development of such a thermal lens. The local thermalresistance, i.e., substantially the quotient of the temperature increaseof the active region of the semiconductor laser diode and the local lossfactor density, is suitably influenced in order to achieve a temperatureprofile, which is as homogeneous as possible, in the lateral andlongitudinal direction in the semiconductor layer sequence 2.

FIGS. 2A and 2B show sectional illustrations of two exemplifiedembodiments of semiconductor laser diodes. Since the heat loss sourcesin the semiconductor layer sequence 2 are limited laterally to theactive region 24 in consideration of expansion effects which result inthe formation of the thermal region of influence defined above in thegeneral part, the semiconductor laser diodes of the followingexemplified embodiments have, compared with the known laser diode chipof FIGS. 1A and 1B, a metallization layer 3 whose width is selected tobe clearly smaller so that the metallization layer 3 no longer extendsover the entire width of the semiconductor layer sequence 2 and thusover the entire top side 20 of the semiconductor layer sequence 2.

Furthermore, the semiconductor cover layer 25 in the exemplifiedembodiments shown hereinafter is formed as a structured,current-supplying semiconductor layer which has a high dopantconcentration of more than 1×10¹⁸ cm⁻³ and thus has a high transverseconductivity. The semiconductor cover layer 25 can, as shown in FIG. 2A,be formed as an individual strip which is contacted by the metallizationlayer 3. Furthermore, it is also possible, as shown in FIG. 2B, to formthe semiconductor cover layer 25 over a large area and to structure itby forming of trenches, so that in addition to the central stripprovided for contacting purposes and contacted by the metallizationlayer 3, non-contacted regions of the semiconductor cover layer 25remain beneath the passivation layer 10. The structuring of thesemiconductor cover layer 25 can be done, e.g., via an etching process,wherein at least approximately 10 μm-wide trenches are produced inaddition to the central strip in order to define the region of thesemiconductor cover layer 25 to be contacted.

In addition to the elements and layers of the semiconductor laser diodeshown here, the diode can also have further features, e.g., trenchesbetween individual emitters or active regions of a semiconductor laserdiode formed as a laser bar for optically and electrically separatingthe individual emitters or even any structuring of the metallizationlayer or the passivation layer to aside from the active region 24.

Exemplified embodiments of semiconductor laser diodes are shownhereinafter which can have a structure in accordance with theexemplified embodiments of FIGS. 2A and 2B. In particular, thesemiconductor laser diodes in accordance with the following exemplifiedembodiments have a structured heat-dissipating layer 4 on the top sideof the semiconductor layer sequence which has a structured metallizationlayer 3. The structured heat-dissipating layer 4 allows heat dissipationfrom the active region 24 with a local thermal resistance which variesin a longitudinal and/or lateral direction.

By the embodiments of the heat-dissipating layer 4 shown hereinafter, itcan be possible to at least partly decouple or separate the electricaland thermal paths in the case of the shown semiconductor laser diodes,whereby the distributions of electrical current and heat flow can beinfluenced within certain limits in a mutually independent manner sothat the respective temperature distribution in the semiconductor layersequence 2 changes independently of the electric parameters and ispreferably homogenized within and in the area surrounding the currentinjection region.

The semiconductor layer sequence 2 has, in the exemplified embodimentsshown hereinafter, a structured, current-supplying semiconductor layer26 which is explained by way of example with the aid of a structuredsemiconductor cover layer 25. Alternatively or in addition thereto,semiconductor layers beneath the semiconductor cover layer 25 and abovethe active region 24 can also be structured in an identical or differentmanner.

Furthermore, the metallization layer 3 on the top side 20 of thesemiconductor layer sequence 2 is used on the one hand to produce ametal-semiconductor contact with the semiconductor cover layer 25 butalso on the other hand to provide a solderable surface by means of whichthe shown semiconductor laser diodes can be mounted on an external heatsink or carrier.

By way of the structuring of the heat-dissipating layer 4 shownhereinafter and optionally also the current-supplying semiconductorlayer 26, these have, at least in some or all three dimensions,laterally, longitudinally and vertically different forms, i.e.,different geometries and/or layer thicknesses which, in addition to theillustrated exemplified embodiments, can also be formed in severalstages or from several different materials.

The exemplified embodiments shown hereinafter each have a metallizationlayer 3 having a cumulative width B1, the ratio of which to the width B2of the thermal region of influence 29 varies in dependence upon thedistance to the radiation coupling-out surface 11.

FIGS. 3A to 3D show exemplified embodiments of semiconductor laserdiodes in which the structured heat-dissipating layer 4 is formed by themetallization layer 3. In the illustrated exemplified embodiments, themetallization layer 3 has a cumulative width B1 which corresponds to thelateral width which becomes smaller as the distance to the radiationcoupling-out surface 11 increases. The current-supplying semiconductorlayer 26 has, in contrast, a width which stays the same, whereby thewidth of the active region 24 and thus also the width B2 of the thermalregion of influence 29 also remains substantially the same in thelongitudinal direction. As a result, the ratio of the cumulative widthB1 of the metallization layer 3 to the width B2 of the thermal region ofinfluence 29 is reduced as the distance to the radiation coupling-outsurface 11 increases.

As shown in FIG. 3A, the metallization layer 3 can have, close to theradiation coupling-out surface 11, a width B1 which is greater than orequal to the width B2 of the thermal region of influence 29 and thusalso greater than the width of the current-supplying semiconductor layer26. As the distance to the radiation coupling-out surface 11 increases,the width B1 of the metallization layer 3 decreases so that themetallization layer 3 is only as wide in the region of the rear surface12 as the current-supplying semiconductor layer 26 and is thus narrowerthan the thermal region of influence 29.

As shown in FIG. 3B, the width B1 of the metallization layer 3 can alsobe reduced to the extent that it is even narrower than the thermalregion of influence 29 in the region of the rear surface 12. Owing tothe high transverse conductivity of the highly doped current-supplyingsemiconductor layer 26, the current is injected into the active layer 23despite the narrower metallization layer 3 and thus the narrower contactregion in the region of the rear surface 12 having a uniform width overthe entire resonator length.

FIG. 3C shows a further exemplified embodiment in which themetallization layer 3 has a width which corresponds in the region of theradiation coupling-out surface 11 to the width of the current-supplyingsemiconductor layer 26 and which is reduced towards the rear surface 12.

FIG. 3D shows a further exemplified embodiment in which themetallization layer 3 has wedge-shaped cut-outs away from the rearsurface 12, whereby the cumulative width B1 of the metallization layer 3is likewise reduced as the distance to the radiation coupling-outsurface 11 increases in comparison with the width B2 of the thermalregion of influence 29.

By reducing the cumulative width B1 of the metallization layer 3 formedas a structured heat-dissipating layer 4 as the distance to theradiation coupling-out surface 11 increases in comparison with the widthB2 of the thermal region of influence 29, the solderable surface andthus also thermal connecting surface of the illustrated semiconductorlaser diodes is reduced as the distance to the radiation coupling-outlayer 11 increases. As a result, in the region of the radiationcoupling-out surface 11 more heat is dissipated than in the region ofthe rear surface 12, whereby the temperature distribution profile in thelongitudinal direction, which is inhomogeneous in known laser diodechips, can be counteracted by a structured local thermal resistance. Inthe case of the semiconductor laser diodes shown in this case, the localthermal resistance in the thermal region of influence 29 is impaired orreduced compared with known laser diode chips in regions having asmaller temperature increase, whereby although the overall temperatureof the active region 24 possibly increases, the effect of the thermallens can be reduced by reducing the inhomogeneous temperaturedistribution.

FIGS. 4A and 4B show further exemplified embodiments of semiconductorlaser diodes in which the current-supplying semiconductor layer 26,i.e., the semiconductor cover layer 25 purely by way of example in theillustrated exemplified embodiments, is structured with respect to itswidth.

In the exemplified embodiment of FIG. 4A, the current-supplyingsemiconductor layer 26, i.e., the semiconductor cover layer 25 in theillustrated exemplified embodiment, has a width which becomes largertowards the radiation coupling-out surface 11. The active region 24resulting therefrom thereby has a trapezoidal shape. Accordingly, athermal region of influence 29, whose width B2 decreases as the distanceto the radiation coupling-out surface 11 increases, is thus also formed.The metallization layer 3 has a width B1 which likewise decreases as thedistance to the radiation coupling-out surface 11 increases, wherein thechange in the width B1 is greater than the change in the width B2 whichmeans that the ratio of the width B1 to the width B2 likewise decreasesas the distance to the radiation coupling-out surface 11 increases.Owing to the described formation of the current-supplying semiconductorlayer 26 and the metallization layer 3, an adaption of the currentinjection to the mode propagation and expansion, and an optimization ofthe current injection profile can be combined with the adapted heatdissipation, described in this case, from the thermal region ofinfluence 29.

In the exemplified embodiment of FIG. 4B, the metallization layer 3 hasa constant cumulative width B1 between the radiation coupling-outsurface 11 and the rear surface 12, whereas the current-supplyingsemiconductor layer 26, i.e., the semiconductor cover layer 25 in theillustrated exemplified embodiment, becomes wider as the distance to theradiation coupling-out surface 11 becomes larger, whereby the width B2of the thermal region of influence 29 also increases as the distance tothe radiation coupling-out surface 11 becomes larger. By way of theinhomogeneous electrical bonding of the active layer 23 or the activeregion 24 to the metallization layer 3 having a constant width and theresulting reduction of the ratio of the widths B1 and B2, the formationof an inhomogeneous temperature distribution with increased temperaturein the region of the radiation coupling-out surface 11 can becounteracted.

The preceding designs for the ratio of the widths B1 and B2 are alsoapplicable for the exemplified embodiments of the following figures, inwhich the widths B1 and B2 are no longer shown for reasons of clarity.

FIG. 5 shows a further exemplified embodiment of a semiconductor laserdiode in which the properties of the metallization layer 3 in accordancewith the exemplified embodiment of FIG. 3A and the properties of thestructured current-supplying semiconductor layer 26 in accordance withthe exemplified embodiment of FIG. 4B are combined in order to achievean improvement of the homogenization of the temperature profile bycombining the described effects.

FIG. 6 shows a further exemplified embodiment of a semiconductor laserdiode in which the metallization layer 3 has, in comparison with theexemplified embodiment of FIG. 5, in addition to a central strip whichis applied for electrically contacting the semiconductor layer sequence2, further strips having the metallization layer material 3. As aresult, an additional solder contact surface is rendered possible asidefrom the thermal region of influence 29.

FIG. 7 shows a further exemplified embodiment of a semiconductor laserdiode in which, in comparison with the exemplified embodiment of FIG. 5,a further semiconductor layer 27 below the structured current-supplyingsemiconductor layer 26, i.e., the semiconductor cover layer 25 in theillustrated exemplified embodiment, has a structured edge in the lateraldirection. FIG. 7 illustrates, purely by way of example, serration-likestructuring. By way of such structuring of the lateral edge of one ormore semiconductor layers 27 below the current-supplying semiconductorlayer 26, the current density profile in the active layer 23 canadditionally be formed.

In the following figures, the thermal region of influence 29 is notshown for reasons of clarity.

FIG. 8 shows a semiconductor laser diode in accordance with a furtherexemplified embodiment which illustrates a further development of theexemplified embodiment shown in FIG. 3B. The current-supplying layer 26is designed purely by way of example with a width which stays the samein the longitudinal direction from the radiation coupling-out surface 11to the rear surface 12, whereas the metallization layer 3 has a centralstrip as the structured heat-dissipating layer 4, the width of thecentral strip decreasing as the distance to the radiation coupling-outsurface 11 increases.

Furthermore, the metallization layer 3 has, in the lateral direction inaddition to the central strip, insular regions 30 o having the materialof the metallization layer 3 so that the metallization layer 3 has anedge in the lateral direction which is structured in an insular manner.In particular, the structuring can be half-tone microstructuring of themetallization layer 3 for the targeted production of hollow spaces orcavities in a solder layer applied thereon or for preventing a solderconnection between a solder and the metallization layer 3, whereby thelocal thermal resistance can be additionally structured. The cumulativewidth of the metallization layer 3 decreases as the distance to theradiation coupling-out surface 11 increases.

The insular structuring 30 can become smaller in the lateral directionwith respect to the size, number and/or density of the islands as thedistance from the central strip increases. In particular, the lateralstructuring can have size and distance ranges in a region of less thanor equal to 1000 μm down to a few micrometers and, in a particularlypreferred manner, greater than or equal to 3 μm. The height of theindividual insular region 30 can be in a size range of greater than orequal to 1 nm to less than or equal to 100 μm. In the region of theinsular structuring 30, in particular a black region denotes a solderconnection and thus a high thermal conductivity whilst a white regiondenotes a non-existing solder connection or a cavity and thus a lowthermal conductivity.

FIGS. 9A to 9C show further exemplified embodiments of semiconductorlaser diodes which, in comparison with the preceding exemplifiedembodiments, have a metallization layer 3 formed as a structuredheat-dissipating layer 4 and comprising openings 31 which take up alarger surface area in terms of their size, number and/or density as thedistance to the radiation coupling-out surface 11 increases, whereby thecumulative width of the metallization layer 3 likewise decreases as thedistance to the radiation coupling-out surface 11 increases. As shown inFIG. 9A, the openings 31 can increase, e.g., in terms of their size asthe distance to the radiation coupling-out surface 11 increases.Therefore, the metallization layer 3 provides overall a flat connectionsurface for solder in which, however, in the region of the openings 31no solder connection or cavity occurs which results in a low thermalconductivity in these regions.

FIG. 9B shows a sectional image in which, in accordance with a furtherexemplified embodiment, a semiconductor laser diode having the substrate1, the semiconductor layer sequence 2 and a metallization layer 3structured with openings 31 in accordance with the preceding exemplifiedembodiment is arranged on an external heat sink 6 by a solder layer 5.The longitudinal resonator direction is perpendicular to the plane ofthe drawing. Owing to the metallization layer 3 formed as a structuredheat-dissipating layer, structuring of the solder boundary surface isproduced in particular owing to the missing metallization in theopenings 31, which, as shown in the illustrated exemplified embodiment,can be further increased by introducing a material 32 into the openings31, which material cannot be soldered or is poorly solderable orconducts heat poorly. For example, poorly solderable metals, e.g.,oxidized metals can be produced or introduced within the openings 31, oreven a material having low thermal conductivity, e.g., air, vacuum or asynthetic material such as for instance BCB. With respect to a possiblyhigh contrast of the thermal conductivity, a metallization layer 3 withopenings 31 filled with air or a vacuum is particularly advantageous. Inmechanically critical chip designs, it is advantageous in terms of agreater mechanical stability to use, instead of openings 31 filled withair or a vacuum, a material 32 which has a thermal conductivity which isas poor as possible and which permits mechanical attachment, i.e., forexample, a synthetic material or a metal oxide which conducts heatpoorly.

In the exemplified embodiment of FIG. 9C, the semiconductor laser diodehas, on the metallization layer 3 which is designed as a structuredheat-dissipating layer 4 as in the preceding exemplified embodiment ofFIG. 9B, an internal heat sink 7 which is applied directly on themetallization layer 3 in direct contact. By way of such an internal heatsink 7 it is possible to lower the overall thermal resistance of thesemiconductor laser diode and despite this thereby to achievestructuring of the local thermal resistance rich in contrast. The sideof the internal heat sink 7 facing away from the semiconductor layersequence 2 is designed as a solder surface for mounting thesemiconductor laser diode on the external heat sink 6 by the solderlayer 5.

The internal heat sink 7 can consist of an individual layer of amaterial or also of several layers. Furthermore, it is also possiblethat the internal heat sink 7 has lateral and/or longitudinalstructuring, as shown in conjunction with the following exemplifiedembodiments.

The internal heat sink 7 can comprise, for example, one or more metals,alloys, dielectric materials, polymers, crystalline semiconductors,amorphous semiconductors, diamond, ceramic material, air, vacuum orcombinations thereof, as described in the general part. The internalheat sink 7 can be applied in particular by vapor deposition,sputtering, galvanic deposition, plasma deposition, spin-coating orbonding. If required, one or more materials or layers of the internalheat sink, as described in the general part, can be encapsulated withrespect to the surroundings, e.g., by a metal which does not react verywell or by a thin-layer encapsulation as described above in the generalpart.

In the following exemplified embodiments, semiconductor laser diodeshaving an additional structured internal heat sink 7 are shown, whichheat sink is formed as part of the structured heat-dissipating layer 4.The semiconductor layer sequence 2 and the metallization layer 3 can bedesigned as in one of the preceding exemplified embodiments. Thestructurings of the internal heat sink 7 in two or three dimensionsshown in the following exemplified embodiments renders it possible toadditionally influence, in a targeted manner, the thermal conductivityin all three dimensions and thus to achieve structuring of the localthermal resistance. In particular, the internal heat sinks 7 shownhereinafter have different regions which consist of different materials71, 72, 73 having different thermal conductivities.

In comparison with conventional heat sinks, which typically have in thevertical direction several metal layers or combinations of metals,semiconductors and/or ceramic materials, e.g., so-called DCB (“directcopper bonded”) consisting of copper and aluminum nitride and which arethus structured vertically, the internal heat sinks 7 shown in this caseare structured laterally and/or longitudinally. The choice of materials71, 72, 73 is not only based, as in the known vertically structured heatsinks, on the producibility or the adjustment of a thermal expansioncoefficient adapted to the semiconductor materials, but also withrespect to the homogenization of the temperature distribution prevailingin the semiconductor material.

In the exemplified embodiment of FIG. 10A, the internal heat sink 7 ofthe semiconductor laser diode has a first material 71 which is arrangedlaterally between regions having a second material 72. The firstmaterial 71 has, in the exemplified embodiment of FIG. 10A and in thefollowing exemplified embodiments of FIGS. 10B to 10H, a higher thermalconductivity than the second material 72, so that preferably heat can bedissipated in the proximity of the active region.

In comparison to the exemplified embodiment of FIG. 10A, thesemiconductor laser diode in accordance with the exemplified embodimentof FIG. 10B has an internal heat sink 7 which, on its sides facingtowards and facing away from the semiconductor layer sequence 2,additionally has the first material 71 above and below the secondmaterial 72, whereby it is possible to achieve a higher thermalconductivity compared with the exemplified embodiment of FIG. 10A.

In the exemplified embodiment in accordance with FIG. 10C, the secondmaterial 72 has additional structuring having a thickness whichincreases outwardly in the lateral direction, whereby the thermalconductivity can be continuously reduced outwardly in the lateraldirection.

In the exemplified embodiment in accordance with FIG. 10D, the firstmaterial 71 has a width which increases as the distance to thesemiconductor layer sequence 2 increases, whereby it is possible toachieve an expansion in the heat flow from the metallization layer 3 toan external heat sink on the side of the internal heat sink facing awayfrom the semiconductor layer sequence 2.

FIG. 10E illustrates a further exemplified embodiment for asemiconductor laser diode in which the first material 71 has a widthwhich becomes smaller as the distance to the radiation coupling-outsurface 11 increases, so that in the region of the radiationcoupling-out surface 11 more heat can be dissipated than in theproximity of the rear surface opposite the radiation coupling-outsurface 11.

In the exemplified embodiment of FIG. 10F, the second material 72 isembedded in a strip-like manner laterally next to the active region ofthe semiconductor layer sequence 2 in the first material 71. The hatchedregions beneath the second material 72 are used merely to more clearlyshow the position of the second material 72 within the first material71.

The internal heat sink 7 in accordance with the exemplified embodimentof FIG. 10G has, in addition to the second material 72, a third material73 which has a different thermal conductivity coefficient compared withthe first and second material 71, 72, whereby the heat dissipation andthe local thermal resistance of the internal heat sink 7 can be adjustedfurther.

Alternatively or in addition to the illustrated exemplified embodimentsin which the second material 72 is arranged continuously in thelongitudinal direction, the second material can, as shown in FIG. 10H,also have structuring in points or in regions. For example, the number,size and/or density of the regions having the second material 72 canincrease in the first material 71 as the distance to the radiationcoupling-out surface 11 increases and/or as the lateral distance to theactive region increases.

FIG. 11 illustrates a further exemplified embodiment of a semiconductorlaser diode having an internal heat sink 7 formed as a structuredheat-dissipating layer 4, which heat sink comprises a structured firstmaterial 71 which is at a distance to the radiation coupling-out surface11 and to the rear surface 12, so that the semiconductor layer sequence2 and the metallization layer 3 form a protrusion over the firstmaterial 71. The protrusion can be produced, for example, bylithographic structuring in an order of magnitude of, e.g., a fewmicrometers and can obviate the need to adjust the semiconductor laserdiode precisely to the edge of an external heat sink or an externalcarrier, which is required in the prior art to ensure sufficient coolingof the radiation coupling-out surface and high reliability associatedtherewith. Since it is also typically required in the prior art toarrange an internal heat sink spaced apart from the radiationcoupling-out surface in order to be able to break the bevel forming theradiation coupling-out surface with a high degree of quality, thecooling at the radiation coupling-out surface is hereby impaired in theprior art.

In order to improve the thermal bonding of the radiation coupling-outsurface 11 and the rear surface 12, in the exemplified embodiment shownin this case, a channel having an effectively heat-conducting secondmaterial 72 is formed in each of these regions so that a self adjustedthermal bonding of the radiation coupling-out surface 11 and the rearsurface 12 can be produced. Such channels can be effected, for example,by applying a deposition having the second material 72 adjoining thefirst material 71, wherein the second material 72 comprises or is amaterial which melts at a low temperature and having good thermalconductivity, e.g., a metal such as indium or tin. Such a deposition ispreferably applied, e.g., by breaking, prior to producing the radiationcoupling-out surface 11 on the relevant regions of a wafer compositeconsisting of a plurality of semiconductor laser diodes which are stillconnected, and is melted, only after separating the semiconductor laserdiodes, by heating to above the melting point of the second material 72to the extent that an automatically adjusting channel is formed. Thechannel can be formed to be concave or convex depending upon thematerial, provided amount, dimensions and process parameters.

The features, described and illustrated in the exemplified embodiments,relating to the structured current-supplying layer, the metallizationlayer and the internal heat sink can also be combined together inaccordance with further exemplified embodiments which are not explicitlyshown in order to combine the respective effects and advantages.

The invention is not limited to the exemplified embodiments by thedescription using same. Rather, the invention includes any new featureand any combination of features what includes in particular anycombination of features in the claims, even if this feature or thiscombination itself is not explicitly stated in the claims or in theexemplified embodiments.

What is claimed is:
 1. A semiconductor laser diode comprising: asemiconductor layer sequence having semiconductor layers disposed oneabove the other including an active layer which comprises an activeregion, the active layer being configured to emit radiation duringoperation via a radiation coupling-out surface, wherein the radiationcoupling-out surface is formed by a lateral surface of the semiconductorlayer sequence and forms, with an opposite rear surface, a resonatorhaving lateral gain-guiding in a longitudinal direction, and wherein thesemiconductor layer sequence is configured to be heated in a thermalregion of influence by reason of the operation; a metallization layer indirect contact with at least a sub-region of a top side of thesemiconductor layer sequence, wherein the top side comprises asemiconductor cover layer, and wherein the metallization layer has acumulative width and a ratio of the cumulative width to a width of thethermal region of influence varies depending on a distance to theradiation coupling-out surface; a structured heat-dissipating layer onthe top side of the semiconductor layer sequence, wherein the structuredheat-dissipating layer comprises at least the metallization layer,wherein the structured heat-dissipating layer allows heat dissipationfrom the active region which varies in a longitudinal and/or a lateraldirection; and an internal heat sink located directly on themetallization layer in direct contact with the metallization layer,wherein the structured heat-dissipating layer comprises the internalheat sink, wherein the internal heat sink has a structuring, whereinstructuring of the internal heat sink comprises materials havingdifferent thermal conductivities, such that the internal heat sink has afirst material which is arranged laterally between regions having asecond material, and wherein the first material has a higher thermalconductivity than the second material.
 2. The semiconductor laser diodeaccording to claim 1, wherein the internal heat sink is disposeddirectly on the metallization layer without a solder connection.
 3. Thesemiconductor laser diode according to claim 1, wherein the ratio of thecumulative width to the width of the thermal region of influencedecreases as the distance to the radiation coupling-out surfaceincreases.
 4. The semiconductor laser diode according to claim 1,wherein the cumulative width of the metallization layer decreases as thedistance to the radiation coupling-out surface increases.
 5. Thesemiconductor laser diode according to claim 1, wherein themetallization layer is wider close to the radiation coupling-out surfacethan the thermal region of influence.
 6. The semiconductor laser diodeaccording to claim 1, wherein the metallization layer is narrower closeto the rear surface than the thermal region of influence.
 7. Thesemiconductor laser diode according to claim 1, wherein themetallization layer has openings, wherein at least one or severalproperties selected from size, number and density of the openingsincrease(s) as the distance to the radiation coupling-out surfaceincreases.
 8. The semiconductor laser diode according to claim 7,wherein a material is arranged in the openings, and wherein the materialhas a lower thermal conductivity and/or a lower solderability than themetallization layer.
 9. The semiconductor laser diode according to claim1, wherein the metallization layer has an edge in the lateral direction,and wherein the edge is structured in an insular manner.
 10. Thesemiconductor laser diode according to claim 1, wherein at least onesemiconductor layer between the semiconductor cover layer and the activelayer have a structured edge in the lateral direction.
 11. Thesemiconductor laser diode according to claim 1, wherein the cover layeris a structured current-supplying semiconductor layer.
 12. Thesemiconductor laser diode according to claim 1, wherein thesemiconductor layer sequence has a semiconductor layer configured tosupply current to the active region between the structuredheat-dissipating layer and the active region, having a width thatincreases at least in a sub-region as the distance to the radiationcoupling-out surface becomes larger.
 13. The semiconductor laser diodeaccording to claim 1, wherein the semiconductor laser diode isconfigured to be mounted on an external carrier by a solder layer via asolder side.
 14. The semiconductor laser diode according to claim 13,wherein the internal heat sink has the solder side facing away from thesemiconductor layer sequence, via which the semiconductor laser diode ismountable on an external carrier by the solder layer.
 15. Thesemiconductor laser diode according to claim 14, wherein the structuredheat-dissipating layer comprises the internal heat sink and the internalheat sink has a structuring at least in the lateral and/or longitudinaldirection.
 16. The semiconductor laser diode according to claim 1,wherein the active region has a width of greater or equal to 30 μm.